Conventionally, a variety of different gases are used in semiconductor production processes, depending on the nature of the individual process. For example, PFC (perfluoro compound) gas, which includes a variety of fluorine-containing compounds such as CF4, NF3, C3F8, SF6 and CHF3, is used as a reactive gas in dry etching processes and thin film formation processes, and an exhaust gas containing this PFC gases is produced.
Exhaust gases such as PFC gas cannot be simply discharged from the system, and must be treated using a variety of treatment methods. Examples of these treatment methods include (i) decomposition treatments in which the PFC gas is decomposed by combustion, catalytic heating, or plasma decomposition or the like, (ii) membrane separation in which the materials are separated by a membrane, (iii) cryogenic separation in which separation is achieved by utilizing differences in the boiling points of the gases, and (iv) adsorption treatments.
However, there are drawbacks associated with decomposition treatments (i) in that achieving complete decomposition is difficult, and the fact that because the gas is decomposed and discharged, it cannot be recovered and reused. Furthermore, although membrane separation (ii) enables the removal of nitrogen from an exhaust gas, the separation of gases of similar molecular size such as CF4 and NF3 is problematic. Moreover, the aforementioned method (iii) requires an extremely large apparatus, and is very expensive in terms of both running costs and the cost of the facilities. Furthermore, the difference in boiling point between NF3 and CF4 is only 1° C., meaning separation of these two gases is very difficult. The method (iv) requires regular replacement of the adsorbent, which leads to costs associated with the disposal of the used adsorbent.
Accordingly, Japanese Patent Laid-Open Publication No. 2002-273144 proposes a device for separating PFC gases that uses a chromatographic separation device packed with an activated carbon filler. The device disclosed in Japanese Patent Laid-Open Publication No. 2002-27314 is able to effectively separate CF4 and NF3.
However, it was found that the device disclosed in Japanese Patent Laid-Open Publication No. 2002-27314 was unable to satisfactorily separate a mixed gas of CF4 and C2F6, for example. As described above, PFC gas contains a variety of different gases, and a unit that is capable of effectively treating and separating this type of multi-component PFC gas has been keenly sought.